Method of making a laminated wood product

ABSTRACT

The present disclosure relates to a method of producing a laminated wood product, comprising providing a plank presenting a pair of parallel major surfaces, a pair of minor surfaces, a pair of end surfaces and a longitudinal direction parallel with said major and minor surfaces and perpendicular to the end surfaces, said plank having a water content of more than 25% by weight, preferably more than 30% by weight, initializing at least one longitudinal crack in the plank, drying said crack initialized plank to a moisture content of less than 20% by weight, and laminating said crack initialized plank by gluing at least one of its major surfaces to a surface of a second member, thus forming the laminated wood product. The disclosure also relates to a laminated wood product, which may be formed according to the method.

This application is a U.S. National Phase under 35 U.S.C. § 371 ofInternational Application No. PCT/IB2017/056647, filed Oct. 26, 2017,which claims priority under 35 U.S.C. §§ 119 and 365 to SwedishApplication No. 1651424-2, filed Oct. 28, 2016.

TECHNICAL FIELD

The present disclosure relates to a method of making a laminated woodproduct, and to a wood product which can be made according to thismethod.

The method is specifically suitable for processing of so-calledhardwood, but may also be used for softwood.

BACKGROUND

One of the most frequently used wood species for construction is spruceor Norway spruce. However, a trend is that the proportion of spruce inEuropean forests is declining.

On the other hand, the proportion of beech, and in particular red beech,is increasing.

As such, beech is attractive, because of its strength properties, whichare actually superior to those of spruce.

Beech, however, exhibits more shrinkage than e.g. spruce and is thusmore prone to deforming (twisting, bowing, cupping, crooking) inconnection with drying than spruce. Hence, dried planks of beech callfor more removal of material in order to achieve planar planks, thancorresponding planks of spruce. Hence, processing of beech is associatedwith greater material losses than processing of spruce.

FIG. 1 illustrates how different plank or rod geometries 1 a, 1 b, 1 c,1 d, 1 e, 1 f may be cut from a piece of raw material in the form of awooden log 1. As is readily visible from FIG. 1, the orientation of theyear rings will differ between different parts of the cross section. Asa consequence, planks or rods cut from different parts of the log willdeform differently as they dry, as indicated in FIG. 1.

FIGS. 2a-2b schematically illustrate how a log 1 is typically cut into aplurality of planks.

As illustrated in FIG. 2a , the log 1 may be cut along a plurality ofparallel longitudinal planes, such that a plurality of wood planks 10are formed.

As illustrated in FIG. 2b , the log 1 may be cut into planks 11 alongone or more first longitudinal planes, and then subsequently along oneor more second longitudinal planes perpendicular to the firstlongitudinal planes. In the embodiment illustrated in FIG. 2b , onefirst longitudinal cutting plane is provided, whereby the log is cut inhalves having a respective semicircular cross section, and subsequentlyeight second longitudinal cutting planes, which are all perpendicular tothe first one, and typically equally spaced from each other.

Again, it can be seen that each plank will have its unique propertiesand thus its unique deformation when drying.

FIG. 3 schematically illustrates a cross section of a cupped plank 10.Such cupping typically occurs during the drying process. From FIG. 3, itcan be deduced how much material would need to be cut away in order toprovide a plank 101 having a rectangular cross section. In reality,losses of about 40-50% are not uncommon.

In view of the above, there is a need for a method which reduces theloss of material and thus allows for more efficient use of beech as aconstruction material.

SUMMARY

An objective of the present disclosure is to provide a method whichreduces the loss of material and thus provides for more efficient use ofbeech, and other hard and soft woods as a construction material.

The invention is defined by the appended independent claims, withembodiments being set forth in the appended dependent claims, in thefollowing description and in the attached drawings.

According to a first aspect, there is provided a method of producing alaminated wood product, comprising providing a plank presenting a pairof parallel major surfaces, a pair of minor surfaces, a pair of endsurfaces and a longitudinal direction parallel with said major and minorsurfaces and perpendicular to the end surfaces, said plank having awater content of more than 25% by weight, preferably more than 30% byweight. Initializing at least one longitudinal crack in the plank,drying said crack initialized plank to a moisture content of less than20% by weight, and laminating said crack initialized plank by gluing atleast one of its major surfaces to a surface of a second member, thusforming the laminated wood product.

Thanks to the invention, a method of controlling the initiation ofcracks in a plank is provided, both with regards to the location of acrack as well as to the number of cracks to be created. In the contextof a log or a plank, the term “longitudinal” is understood to refer to adirection which is substantially parallel with a main fiber direction ofsuch log or plank. The term “substantial” here reflects that fibers arenot always perfectly straight throughout the log or plank, and thatthere may be local variations in fiber direction, e.g. due to knots orother defects.

Moreover, in the context of a plank, the term “width” is understood torefer to a direction that is perpendicular to the longitudinaldirection, parallel with a major cut surface of the plank.

In the context of a plank, the term “thickness” is understood to referto a direction which is perpendicular to the major cut surface of theplank.

A “plank” is a typically elongate piece of sawn lumber, which is formedof one piece of lumber and which is integral. That is, all pieces makingup a plank remain connected, albeit with cracks and partial separations,and thus have not been artificially joined together.

Water content is expressed herein in the, for wood, conventional way,i.e. in proportion to the dry weight of the wood. That is moisturecontent=(wet weight−dry weight)/(dry weight).

An initialized crack means that the plank has been provided with a notchor dent from which a crack may start propagating.

The second member may be one or more planks, a wood fiber based board, achipboard, a film, a web, etc.

The invention is based on the insight that, in many circumstances,longitudinal cracks are more of an optical, or aesthetic, problem, thana strength problem.

Hence, in a laminated structure, where some or all lamellae havelongitudinal cracks, the strength properties may nevertheless be equal,or close to equal, to a laminated structure lamellae that arenon-cracked. Hence, the cracks do not prevent the fiber strength frombeing utilized.

By initiating cracks, and incorporating these initiated cracks in thelaminated product when the product is being laminated in wet state, thedeformation that normally takes place during drying will have little orno effect on the finished product.

Moreover, by initiating cracks in sawn goods and allowing cracks to formduring drying, the overall yield may be increased.

In addition, cracked planks may allow for faster drying.

The initializing may comprise wedging into the plank.

The wedging may be performed towards at least one of the end surfaces.

In particular, the wedging may comprise applying a force by a wedgemember in a direction+/−45°, preferably +/−30°, +/−10° or approximatelyperpendicular, to a surface normal of the end surfaces.

The wedging may be performed with a wedge edge, which is orientedsubstantially perpendicular to the major surfaces.

In one example, the wedging may be performed with a wedge edge, which isoriented substantially perpendicular to a year ring tangent where thewedge engages the end surface.

The wedge edge may be driven into the end surface less than 5% of aplank length, preferably less than 1% or less than 0.1% of the planklength.

In reality, the wedges may be driven only a few centimeters, or evenmillimeters, into the end surface.

As an alternative, or supplement, the initializing may compriseproviding a longitudinal notch in at least one of the major surfaces.

The longitudinal notch may comprise wedging or cutting into the majorsurface.

The longitudinal notch may comprise sawing or milling into the majorsurface.

The notch may be continuous over at least 50% of a length of the plank,preferably over at least 70% or at least 90%.

The notch may be discontinuous and presents at least two aligned notchsections of less than 45% of a length of the plank, preferably less than30% or less than 10%.

The notch sections may be aligned longitudinally along the plank, oralong a feature of the plank, such as a year ring or a fiber.

A notch depth may be less than 90% of a plank thickness, preferably lessthan 30%, less than 20% or less than 10%.

In reality, notch depth may be on the order of 0.5-5 mm.

The method may further comprise measuring a wedging force, whereby thewedging may be performed until the wedging force starts decreasing.

As another option, the initializing may comprise cutting into the plank.

The cutting may comprise removing material in the form of dust or chips.

The cutting may be performed towards an end surface of the plank.

Alternatively, or as a supplement, the cutting may be performed towardsa major surface of the plank.

At least two laterally spaced cracks may be initiated along respectivelongitudinal directions of one major surface.

The cracks may be spaced apart by a distance corresponding to athickness of the plank+/−25%, preferably +/−10%.

The method may further comprise obtaining data on fiber directions of atleast part of the at least one of the major surfaces and initiating atleast one crack parallel with such fiber direction.

The method may further comprise opening at least one initiated crack.

Such opening may comprise applying a torque about an axis parallel withthe longitudinal direction of the plank.

The plank may, prior to said drying, have a water content of less than40% by weight, preferably less than 35% by weight.

That is, free water may already have been removed, leaving bound wateronly.

In one embodiment, the laminating may be performed before the dryingstep.

The second member may present a water content of less than 25% byweight, preferably less than 20% by weight.

Alternatively, the second member may present a water content of morethan 25% by weight, preferably more than 30% by weight.

The method may further comprise a sanding step and/or a planing step ofat least one of the major surfaces after the drying and prior to thelaminating.

In another embodiment, the laminating may be performed after the dryingstep.

Alternatively, the second member may present a water content of lessthan 25% by weight, preferably less than 20% by weight.

The plank may be formed of hardwood, i.e. from an angiosperm treespecies, having a dry wood density of more than 400 kg/m³.

“Dry wood” is defined as wood having a moisture content that is typicalto commercial lumber, i.e. wood which has been air-dried or kiln-dried.Usually this moisture content may be on the order of 8-18% by weight.

According to a second aspect, there is provided a laminated woodproduct, comprising a first layer which is formed of at least onehardwood plank presenting a pair of parallel major surfaces, a pair ofminor surfaces, a pair of end surfaces and a longitudinal directionparallel with said major and minor surfaces and perpendicular to the endsurfaces, said plank having a water content of less than 25% by weight,and said plank presents a pair of juxtaposed plank portions, at leastpartially separated by an open gap running along a fiber direction ofthe plank, said gap presenting crack surfaces; and at least one secondlayer, laminated to the major surface.

A crack surface is a surface of a crack or split of the wood, and may berecognized in that it is generally irregular and generally follows thefiber direction of the wood without cutting off the fibers. Cracks andsplits are characterized in that originally adjacent wood fibers havebeen separated in a direction perpendicular to their longitudinaldirections without removal of material.

It is to be understood that an “open gap” herein refers to that thecrack surfaces are physically separated by said gap, i.e. at theposition of a gap the respective crack surfaces are not connected toeach other for example by means of any filling material or substance.

The crack may present a depth from at least one major surface of 5-100%of a thickness of the plank, preferably of 5-90% of a more preferably10-50%.

The laminated wood product may further comprise at least two secondlayers, which sandwich said plank. The two second sandwiching layers maybe non-cracked. The at least two second layers may present fiberdirections which are substantially perpendicular to the fiber directionof the plank.

In one embodiment a plank forming part of the second layer may extendacross the gap. That is, a plank forming part of the second layer may beoffset in its width direction relative to the plank of the first layer.

Alternatively, at least two second layers may present fiber directionswhich are substantially parallel to the fiber direction of the plank.

In one embodiment, said gap running along a fiber direction of the plankis an open crack, meaning that a non-filled gap is created between thetwo inner longitudinal side surfaces of a crack. It is to be understoodthat “non-filled” is to be interpreted as “empty” or “void of anyfilling material or substance”. An embodiment wherein the cracks areunfilled leads to the advantage that any natural dimensional changes ofthe wood e.g. in the form of shrinking and swelling caused by changes inhumidity are tolerated thus avoiding undesired tension in the plankand/or the upcome of uncontrolled cracks. By providing open spacesinside the planks, any swelling or shrinking will mainly occur insidethe plank and build-up of tensions in the material is minimized. Alsothe fact that the cracks are open leads to that water vapor may beventilated through the air inside the cracks to/from the wood tissueupon humidity changes.

Thanks to the invention there is provided a wood product with animproved tolerability of variations in humidity while at the same timenot reducing the strength properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view of a log.

FIGS. 2a-2b are schematic cross sectional views of a log, which has beencut into a plurality of planks.

FIG. 3 is a schematic cross sectional view of a cupped plank.

FIG. 4a is a schematic cross sectional view of a plank.

FIGS. 4b-4d are schematic planar views of the plank illustrated in FIG.4 a.

FIGS. 5a-5c are schematic planar views of a plank.

FIG. 6a is a schematic perspective view of a first device for initiatinga crack.

FIG. 6b is a schematic perspective view of a second device forinitiating a crack.

FIG. 7 is a schematic planar view of a third device for initiating acrack.

FIG. 8 is a schematic view of a first principle for initiating cracks.

FIG. 9 is a schematic view of a second principle for initiating cracks.

FIG. 10 is a schematic perspective view of a fourth device forinitiating a crack.

FIG. 11 is a schematic perspective view of a fifth device for initiatinga crack.

FIG. 12a-12b is a schematic perspective view of a sixth device forinitiating a crack.

FIG. 13 is a schematic perspective view of a first device for cracking aplank.

FIG. 14 is a schematic perspective view of a second device for crackinga plank.

FIG. 15 is a schematic perspective view of a third device for cracking aplank.

FIG. 16 is a schematic perspective view of cross laminated timbermaterial (CLT) comprising cracked boards in a middle layer.

FIG. 17 is a schematic perspective view of a parallel laminated woodproduct.

FIG. 18 is a schematic perspective view of a laminated wood beam.

DETAILED DESCRIPTION

FIGS. 4a-4d and 5a-5b show a strategy to increase the overall yield: Ifyou would leave the boards intact (FIG. 4b ) there will be no twoidentical boards, so it will be very difficult to fit them together intoa layer with small gaps. Normally you would trim the edges to get boardswith parallel edges. On the other hand most boards can be splitsymmetrically in the middle, so that the two halves can be fit togethernicely, as illustrated, which results in a layer where you have rathersmall gaps between the boards and small trimming waste.

FIGS. 4a-4d schematically illustrate how an approximately trapezoidalplank 20 may be cut longitudinally and rearranged in order to provide anapproximately rectangular aggregate panel.

For example, the plank 20 may be cut along a longitudinal line, therebyforming a pair of plank pieces 21 a, 21 b. By shifting positions of theplank pieces 21 a, 21 b such that their rounded edges face each otherand also turning one of the plank pieces 21 b about 180° about an axisthat is parallel with the plank's 21 b width direction W (and thusperpendicular to its length direction), the plank pieces may be arrangedwith their respective longitudinal cut edges parallel and with a minimumgap between the plank pieces 21 a, 21 b. Moreover, the rounded edges 22a, 22 b may wholly or partially overlap each other.

FIGS. 5a-5c schematically illustrate how a bent plank 30 may be cut andrearranged to provide an approximately rectangular aggregate panel.

For example, the plank 30 may be cut along a longitudinal line to form apair of plank pieces 31 a, 31 b of which one has a convex longitudinaledge 32 a and the other one has a concave longitudinal edge 32 b.

By shifting positions of the plank pieces 31 a, 31 b such that theirrounded edges face each other and also turning one of the plank pieces31 b about 180° about an axis that is parallel with the plank's 31 bwidth direction W (and thus perpendicular to its length direction), theplank pieces may be arranged with their respective longitudinal cutedges parallel and with a minimum gap between the plank pieces 31 a, 31b. Moreover, the rounded edges 32 a, 32 b may wholly or partiallyoverlap each other. The principles of FIGS. 4a-4d and 5a-5c can be usedin order to optimize use of planks when forming, in particular, crosslaminated timber products.

A plank typically presents a pair of substantially planar, mutuallyparallel major surfaces, a pair of minor surfaces and a pair of endsurfaces. A longitudinal direction L is defined as the direction betweenthe end surfaces. Hence, the major surfaces extend substantiallyparallel with the longitudinal direction, as do the minor surfaces.

The plank has a thickness direction T, perpendicular to the majorsurfaces and a width W, perpendicular to both the major surfaces and tothe thickness.

Plank length (L direction) may be on the order of 200-10000 mm, mostoften about 1000-5000 mm. Plank thickness (T direction) may be on theorder of 5-50 mm, most often about 10-40 mm. Plank width (W direction)may be on the order of 30-1000 mm, most often about 50-500 mm.

The plank's major surfaces may be rectangular or trapezoidal in shape.

The minor surfaces, may, but need not be mutually parallel.

A principal fiber direction of the plank may extend substantiallyparallel with the longitudinal direction, i.e. parallel+/−20°,preferably +/−10° or +/−5°.

The end surfaces may be substantially perpendicular to at least one ofthe major and minor surfaces.

The description will now focus on a concept of forming a laminated woodproduct.

Starting from a plank, which may be provided according to e.g. FIG. 2aor FIG. 2b , one or more longitudinal cracks are initiated andoptionally opened. A longitudinal crack may be defined as a crack thatextends along the longitudinal direction of the plank. Preferably, sucha crack will propagate along a fiber direction of the plank, along thelength direction and/or along the thickness direction.

In one alternative, the crack initialized, or cracked, plank may belaminated to at least one second layer when wet, as defined above, orafter a drying step. In this variant, the plank members, to whom theplank is laminated may be dry or wet. The laminated product may then besubject to drying.

In another alternative, the crack initialized, or cracked, plank may bedried prior to lamination. In the latter case, the plank may needformatting, such as sanding and/or planing in order to restore asufficiently planar shape to allow for lamination.

A cracked or crack-initiated plank is much more flexible than anon-cracked plank. In a planing machine the cracked plank can be pressedflat and the planing losses can thus be made much smaller compared to aconventional plank.

To this end, a planing step may be combined with a pressing step,wherein the plank is pressed, e.g. by a calendar arrangement, in thethickness direction while being planed. For example, a first set ofcalendar rolls may be arranged immediately upstream of the planing tooland a second set of calendar rolls may be arranged downstream of theplaning tool.

Drying may also be performed in the conventional manner, such as kilndrying.

The thus crack initiated, or cracked, plank 10′ may be included, alone,or arranged coplanarly with other planks 10′, 12, as a layer L1 of alaminated wood product 1000, as shown in FIG. 16. In FIG. 16 there isseen an example of a laminated wood product 1000 according to theinvention, wherein a middle layer L1 is made up by crack initiated orcracked boards 10′, and adjacent, sandwiching outer layers L2, L3 aremade from non-cracked planks.

As mentioned, the planks 10′ may optionally have its initiated cracksopened, or completed. However, it is preferred that cracks are onlyopened or completed to an extent that allows the plank to still form onepiece. That is, portions of the plank situated on different sides of alongitudinal crack should remain held together.

Lamination of the crack initiated or cracked planks 10′ may be performedin conventional manner.

The lamination may take place using adhesive selected for the particularsystem that is to be laminated. For example, where at least one of theplanks 10′ that is to be laminated is wet, a wet gluing system may beused, such as polyurethane based glue.

The lamination may be supplemented by further measures, such asapplication of pressure, in particular in a direction perpendicular to alamination plane (here the major surfaces), to the laminate inconnection with the drying, setting or hardening of the adhesive.

In connection with the lamination, a catalyst or other reactioninitiating measures may be supplied, such as radiation (UV light), heator water (which is used in polyurethane systems).

That is, a plurality of crack initiated or cracked planks 10′, 10″ maybe arranged coplanarly side by side, optionally with a minor gap betweenadjacent plank edges, whereby major surfaces of the planks 10′ arelaminated to major surfaces of further layers L2, L3.

The further layers L2, L3, L4 may comprise further crack initiated orcracked planks 10′, 10″, which may be arranged with their longitudinaldirections parallel to the planks, but shifted laterally (in the widthdirection W), such that each crack/gap is bridged by the further plank.This is illustrated by the product 1001 in FIG. 17.

Alternatively, the further layers L2, L3 may comprise further crackinitiated or cracked planks 10′, 10″, which may be arranged with theirlongitudinal directions at an angle other than parallel, such asperpendicular, to the planks, such that a cross laminated wood productis provided. This is illustrated in FIG. 16.

As yet further alternatives, one or more of the further layer(s) L2, L3may comprise or consist of planks 12 that are neither (deliberately)cracked nor crack initiated, as illustrated in FIG. 16.

As yet another alternative, cracked or crack initiated planks 10′, 10″may be laminated major surface to major surface to provide a beam 1002,as illustrated in FIG. 18. In such a beam, some planks may be cracked orcrack initiated and others may not be. For example outermost planks, asseen in the thickness direction T, may, for aesthetic reasons, benon-cracked.

The further layers with which the cracked or crack initiated planks arelaminated may comprise, or consist of, other cracked or crack initiatedplanks, normal planks or board materials, such as fiber board, chipboard, MDF, HDF or even polymer films, woven or non-woven webs orplastic sheets.

The description will now focus on the steps of initializing and openingcracks.

FIGS. 6-12 b illustrate various ways of artificially initiating a crackin a wood plank.

FIGS. 6-9 illustrate various ways of initiating a longitudinal crack bywedging or cutting into a short edge of the plank.

In FIG. 6a , there is illustrated a trapezoidal (with respect to majorsurface shape) plank 10 and a plurality of wedging tools 5, 6. At themajor short edge of the plank, three wedging tools 5 may be applied,each having a respective wedge edge 51, which extends perpendicular tothe major surfaces of the plank, and which is driven into at least oneend surface of the plank, substantially along the longitudinaldirection.

It is understood that the wedge edge 51 may be oriented at an angle, asseen in a plane perpendicular to the major surface and to the shortedges (i.e. a L-T plane) other than perpendicular to the end surface. Itis also understood that the wedge may be driven in a direction which isnot perpendicular to the end surface. Moreover, the wedge edge may belinear in shape, or it may be pointed, convex, concave, etc.

An extent of this wedging may be on the order of one or a fewmillimeters, up to one or a few (typically less than 5) centimeters, asthe purpose may be to only initiate a crack, but not to complete it suchthat the pieces on opposite sides of the crack would separate.

Hence, it may be preferred to stop driving the wedge 5, 6 before a crackstarts propagating from the notch formed by the wedge, or immediately ondetection of a start of such propagation.

As illustrated in FIG. 6a , more than one crack may be initiated, suchthat multiple longitudinal cracks are provided.

Cracks may typically be initiated with a spacing, as seen in a directionW transversely of the longitudinal direction L, of 50-200% of athickness T of the plank, preferably about 50-150%, 75-150% or 100-150%of such thickness T.

As illustrated in FIG. 6a , cracks C1, C2, C3 may, but need not, beinitiated from both ends of a plank 10. In the illustrated example,three cracks are initiated by first wedging tools 5 from the major endsurface and two cracks are initiated by second wedging tools 6 from theminor end surface. Hence, the number of cracks initiated at a minor endsurface may be on the order of n−a, where n is the number of cracksinitiated at the major end surface and a is an integer value of 0-3.

Referring to FIG. 7, there is illustrated a case where the number of ais 0, that is, the number of cracks C1, C2, C3 initiated at each shortedge are the same. Other than that, the device illustrated in FIG. 7operates in the same manner as that of FIG. 6 a.

Referring to FIG. 6b , there is illustrated another way of initiatingcracks.

Here, cracks are initiated on the major surfaces using a device, whereinone or more wedging tools 6′ are caused to perform an oscillating motionin a direction perpendicular to the major surfaces. That is, the wedgingtools 6′ will reciprocate towards and away from the major surface,forming, at each cycle, a longitudinally extending elongate dent in themajor surface.

The wedging tools 6′ may have their wedge edges 62 parallel with thelongitudinal direction L, and optionally also with the major surfacetowards which it is to act.

Longitudinal spacing of such dents may be varied by varying theoscillation frequency and/or the speed with which the plank is being fedpast the wedging tool. Hence, it is possible to provide everything froma continuous groove along the length of the plank to one or a fewseparate dents along the length of each plank.

Optionally, the wedging tools may be controllably movable in thetransverse direction, such that the groove formed by each wedging toolmay follow fibers of the wood.

As yet another option, the wedging tools may be rotatable about an axisperpendicular to the major surface, such that the orientation of thewedge edge 62 may be tuned to follow fiber direction in the majorsurface. The rotation may be limited to +/−20°, +/−10° or +/−5°,relative to the longitudinal axis L.

It is noted that methods, e.g. based on image analysis, of determiningfiber direction are known.

Such wedging tools may be provided to operate on one or both majorsurfaces of the plank.

FIG. 8 illustrates a first principle of orienting the wedge edges inFIG. 6 or 7. Here, the wedge edges are aligned with year ring radii ofthe plank, or actually of the log from which the plank was formed. Forexample, it is possible to achieve this by analyzing curvature of yearrings of the plank, derive a tangent of each year ring at each lateralposition where a crack is to be initiated, and to align the wedge edge51, 61 such that it is perpendicular to the tangent of the year ring atthat position.

This mimics the natural cracking of a wood log, which is caused bydifferences in drying-induced shrinking at different radial portions ofthe log 1.

FIG. 9 illustrates the principle used in FIGS. 6a and 7. That is, thewedge edges 51, 61 are simply arranged perpendicular to the majorsurface.

FIGS. 10-12 b illustrate various ways of initiating a longitudinal crackby wedging or cutting into a major surface of the plank.

In FIG. 10, there is illustrated a first way of wedging into a majorsurface of the plank.

As illustrated in FIG. 10, it is possible cause at least one calendar 9a, 9 b having a cutting edge 911, 921 extending along a portion of itscircumference to interact with a major surface of the plank while theplank and the calendar 9 a, 9 b move relative each other.

In the illustrated embodiment, it is contemplated that the calendar 9 a,9 b is stationary and rotatable, whereby the plank is passed by it whilebeing pressed against the calendar. However, it is possible to keep theplank stationary and move the calendar(s) instead.

Moreover, it is contemplated to provide a pair of calendars 9 a, 9 b,each having such partially circumferential cutting edges 911, 921.

In such a device, the plank may be propelled by the calendars 9 a, 9 b,and both surfaces may be crack-initiated at the same time.

As mentioned, each calendar 9 a, 9 b may comprise at least onecircumferential cutting edge 911, 921. However, it may be rational toprovide more such circumferential cutting edges 911, 921.

For example, a first set 91 of partially circumferential cutting edges911 may be axially aligned and spaced from each other.

An axial spacing between adjacent cutting edges 911 may be on the orderof the crack spacing mentioned above, as seen in a direction Wtransversely of the longitudinal direction L. That is 50-200% of athickness T of the plank, preferably about 50-150%, 75-150% or 100-150%of such thickness T.

One or more further sets 92 of partially circumferential cutting edges921 may be axially aligned and spaced from each other, and optionallyaxially offset from the first set 91. Preferably, this further set mayalso be angularly offset from the first set.

For example, each partially circumferential cutting edge 911, 921 mayextend over a portion of the circumference corresponding to about10°-45° angle about a central axis of the calendar. That is, a length ofthe cutting edge 911, 921 may correspond to about 10°-45° of the centralangle.

A circumferential offset between two adjacent sets 91, 92 of cuttingedges 911, 921 may be on the order of 50-150% of the cutting edgelength.

One or both calendars 9 a, 9 b may be provided with cutting edges 911,921.

Hence, in one embodiment, both calendars 9 a, 9 b have cutting edges911, 921, as illustrated in FIG. 10.

In another embodiment, only one of the calendars have cutting edges,while the other one merely provides support and assists in driving theplank, and pressing it towards the calendar having cutting edges.

In FIG. 11, there is illustrated another way of initiating cracks C1,C2, C3.

Here, each crack initiating tool 7 is formed by a rotatable cuttingdisk, having a continuous (possibly non-serrated) cutting edge 71,which, depending on its sharpness and the force applied, wedges intoand/or cuts into at least one of the major surfaces of the plank 10. Inthe illustrated example, a respective set of tools is operable on eachmajor surface of the plank 10.

This cutting edge 71 may be caused to move relative to the plank in asubstantially slip-free manner, i.e. there is no relative movementbetween the cutting disk edge 71 and the plank 10.

Optionally, the cutting disks 7 may be controllably movable in thetransverse direction, such that the groove or cut formed by eachgrooving tool may follow fibers of the wood.

The cutting disks 7 may be individually rotatable, each independentlywith regard to other disks on the same axle 72 or major surface, orrotatable as a group on a common axle.

A common denominator of the methods illustrated in FIGS. 10 and 11, andalso FIGS. 6 and 7 is the absence of removal of material.

In FIG. 12a , there is illustrated yet another way of initiating cracks.

Here, a plurality of rotatable saw blades 8 are provided, each of whichpresenting a saw edge 81 for cutting a shallow groove in the majorsurface of the plank. Thus, material is being removed from thesegrooves.

Optionally, the saw blades 8 may be controllably movable in thetransverse direction, such that the groove formed by each saw blade 7may follow fibers of the wood.

The saw blades 8 may be individually rotatable, each independently withregard to other disks on the same axle or major surface, or rotatable asa group on a common axle 82.

As illustrated in FIG. 12a , the cutting depth may be relativelyshallow, preferably on the order of 5-35%, preferably 5-25%, of thethickness of the plank. This way, the amount of material removed isreduced.

Referring to FIG. 12b , cutting depth of the saw blades 8 may be as muchas 50-90% of the thickness of the plank 10, possibly 70-90% or 80-90%.

Hence, the cuts C1′, C2′ may extend over more than half of the plankthickness, which will further facilitate any subsequent crackingprocess.

The description will now focus on how to wholly or partially open orcomplete longitudinal cracks in a plank. Each of the opening methodsdisclosed below may be used with any of the crack initiation methodsdisclosed above.

Referring to FIG. 13, there is illustrated a first device for opening,or completing, cracks. This device comprises at least two pairs 93 a, 93b, 93 c of rollers 93 a 1, 93 a 2; 93 b 1, 93 b 2; 93 c 1, 93 c 2,wherein the rollers 93 a 1, 93 a 2 of a first pair 93 a are rotatableabout first mutually parallel axes 93 a 3, 93 a 4 and wherein therollers 93 b 1, 93 b 2 of the second pair are rotatable about secondmutually parallel axes. The first and second parallel axes 93 b 3, 93 b4 present an angle of 5°-45°, preferably 10°-30°.

The pairs 93 a, 93 b, 93 c of rollers simultaneously engage laterally(in the W direction) juxtaposed portions of the plank 10, 10′, typically(but not necessarily) a crack-initiated plank 10′, such that a bendingtorque is applied to the plank about an axis parallel with thelongitudinal direction L of the plank.

The plank 10′ is fed along its longitudinal direction L through theroller pairs 93 a, 93 b, 93 c, and is thus successively bent and thuscracked.

The plank may optionally be passed through at least two successive setof rollers, wherein the angle between the axes of the roller setsgradually increase.

When the plank 10″ has been passed through the device of FIG. 13, itwill typically be cracked. However, as mentioned, it is desirable, andthe device may be accordingly adjusted, only to crack the plank to suchan extent that it still forms an integral piece of material.

Referring to FIG. 14, there is illustrated a second device for openingcracks. This device comprises at least three rollers 94 a, 94 b, 94 c,one of which 94 a arranged to engage a first major surface of the plankand the others 94 b, 94 c arranged to simultaneously engage the secondmajor surface of the plank, which may be pristine or crack-initiated.

The rollers 94 a, 94 b, 94 c are arranged such that a line that tangentsboth second rollers 94 b, 94 c at points facing the first roller 94 apresents a minimum distance to the periphery of the first roller 94 a,which minimum distance is less than a thickness of the plank that is tobe processed, preferably less than 75% of said thickness or less than50% of said thickness. The distance may be zero or negative. That is,the periphery of the first roller may tangent or intersect said line.

The plank 10, 10′ may be passed through the rollers along itstransversal direction. The rollers may be of length equal to the plank.

When the plank 10″ has been passed through the device of FIG. 13, itwill typically be cracked. However, as mentioned, it is desirable onlyto crack the plank to such an extent that it still forms an integralpiece of material. In the alternative, two or more sets of spaced apartrollers may be provided.

Referring to FIG. 15, there is illustrated a third device 95 for openingcracks. This device comprises a pair of profiled members 95 a, 95 b, one95 b of which being concave and the other one 95 a being convex.

The profiled members 95 a, 95 b may be provided as a pressing tool,wherein one or more planks 10, 10′ are cracked in each cycle.

Alternatively, the profiled members 95 a, 95 b may be formed as rollers,whereby the plank 10, 10′ may be passed between the rollers in a mannersimilar to that illustrated in FIG. 13.

The invention claimed is:
 1. A method of producing a laminated woodproduct comprising: providing a plank presenting a pair of parallelmajor surfaces, a pair of minor surfaces, a pair of end surfaces and alongitudinal direction parallel with said major and minor surfaces andperpendicular to the end surfaces, said plank having a water content ofmore than 25% by weight, initializing at least one longitudinal crack inthe plank, forming a crack initialized plank, drying said crackinitialized plank to a moisture content of less than 20% by weight, andlaminating said crack initialized plank by gluing at least one of itsmajor surfaces to a surface of a second member, thus forming thelaminated wood product.
 2. The method as claimed in claim 1, whereinsaid initializing comprises wedging into the plank.
 3. The method asclaimed in claim 2, wherein the wedging is performed towards at leastone of the end surfaces.
 4. The method as claimed in claim 2 whereinsaid wedging is performed with a wedge edge, which is orientedsubstantially perpendicular to the major surfaces.
 5. The method asclaimed in claim 2, wherein said wedging is performed with a wedge edge,which is oriented substantially perpendicular to a year ring tangentwhere the wedge edge engages the end surface.
 6. The method as claimedin claim 2, wherein a wedge edge is driven into the end surface lessthan 5% of a plank length.
 7. The method as claimed in claim 1, whereinsaid initializing comprises providing a longitudinal notch in at leastone of the major surfaces.
 8. The method as claimed in claim 7, whereinproviding the longitudinal notch comprises wedging or cutting into themajor surface.
 9. The method as claimed in claim 7, wherein providingthe longitudinal notch comprises sawing or milling into the majorsurface.
 10. The method as claimed in claim 7 wherein the notch iscontinuous over at least 50% of a length of the plank.
 11. The method asclaimed in claim 7, wherein the notch is discontinuous and presents atleast two aligned notch sections of less than 45% of a length of theplank.
 12. The method as claimed in claim 7, wherein a notch depth isless than 90% of a plank thickness.
 13. The method as claimed in claim2, further comprising measuring a wedging force, wherein said wedging isperformed until the wedging force starts decreasing.
 14. The method asclaimed in claim 1, wherein said initializing comprises cutting into theplank.
 15. The method as claimed in claim 14, wherein the cuttingcomprises removing material in a form of dust or chips.
 16. The methodas claimed in claim 14, wherein the cutting is performed towards an endsurface of the plank.
 17. The method as claimed in claim 14, wherein thecutting is performed towards a major surface of the plank.
 18. Themethod as claimed in claim 1, wherein at least two laterally spacedcracks are initiated along respective substantially longitudinaldirections of one major surface.
 19. The method as claimed in claim 18,wherein the at least two laterally spaced cracks are spaced apart by adistance corresponding to a thickness of the plank+/−25%.
 20. The methodas claimed in claim 1, further comprising obtaining data on fiberdirections of at least part of the at least one of the major surfacesand initiating at least one crack parallel with such fiber direction.21. The method as claimed in claim 1, further comprising opening atleast one initiated crack, forming an opening.
 22. The method as claimedin claim 21, wherein said opening comprises applying a torque about anaxis parallel with the longitudinal direction of the plank.
 23. Themethod as claimed in claim 1, wherein the plank, prior to said drying,has a water content of less than 40% by weight.
 24. The method asclaimed in claim 1, wherein the laminating is performed before thedrying step.
 25. The method as claimed in claim 1, wherein the secondmember presents a water content of less than 25% by weight.
 26. Themethod as claimed in claim 1, wherein the second member presents a watercontent of more than 25% by weight.
 27. The method as claimed in claim1, further comprising a sanding step and/or a planing step of at leastone of the major surfaces after the drying and prior to the laminating.28. The method as claimed in claim 1, wherein the laminating isperformed after the drying step.
 29. The method as claimed in claim 27,wherein the second member presents a water content of less than 25% byweight.
 30. The method as claimed in claim 1, wherein the plank isformed of hardwood, having a dry wood density of more than 400 kg/m3, orfrom softwood.